Galloway, Jenna L Project Summary Tendons make essential connections between the forming musculoskeletal tissues, enabling coordinated movement. Disruption to the development and patterning of the musculoskeletal system can result in skeletal malformations or contractures, a congenital abnormality that results in constriction in the movement of joints. In adults, musculoskeletal injuries are common among active individuals and the aging population. Tendon injuries, in particular, are complicated by a slow and limited healing, which can pose significant mobility, pain, and quality of life issues. Comprehensive knowledge of the molecular pathways that guide tendon development and regeneration would have broad impact in our understanding of the etiology of congenital defects as well as in regenerative medicine approaches to tendon injuries. This proposal aims to use the zebrafish to understand the mechanisms underlying tendon cell regeneration and the re-establishment of attachment site pattern. Our previous studies have shown that zebrafish and mammalian tendons are similar in gene expression, developmental regulation, and ultrastructural properties, making them an excellent genetic system for studying tendon biology. We also find zebrafish have robust abilities to regenerate their tendon tissue unlike adult mammals. Building from this novel work, we propose to use a genetic cell ablation model to dissect the cellular and molecular mechanisms underlying tendon regeneration and the restoration of the attachment pattern. We will identify the source of the newly regenerating tendon cells using cell proliferation assays, genetic lineage tracing, and live imaging. Examination of BMP Responsive Element transgenic zebrafish and functional analysis indicate BMP signaling in the regeneration of specific attachment sites. In addition, a high-throughput chemical screen identified compounds with tendon promoting activities and whose targets may intersect the BMP pathway. Using chemical and genetic functional assays, we will dissect the role of BMP signaling in tendon regeneration and the re-establishment of a specific attachment site. We will also test if the chemicals and the pathways they target can augment the regenerative response through their potential intersection with the BMP pathway. Our proposal combines novel tools with live imaging and functional studies and together, this will provide unprecedented visualization of tendon cell behaviors during regeneration. We believe these studies will add crucial insight into tendon development and regeneration, which could impact our understanding of congenital disorders and regenerative medicine approaches to tendon injuries.